Electrical stimulation of biological tissue in humans and non-human animals has applications for stimulating excitable tissue (neurons, muscle, cardiac tissue, etc.) in both transdermal (i.e. transcutaneous) and implanted configurations. Electrodes that improve the comfort, targeting, and/or efficiency of electrical stimulation of tissue are desired so that more precise, more comfortable, more long-lasting, and/or more power-efficient stimulation can be achieved.
Ideally, transdermal electrical stimulation electrodes deliver current in a manner that minimizes skin irritation and pain to the user or patient. Techniques for improving the comfort and safety of transdermal electrical stimulation including using electrodes that (more) evenly distribute current across the dermal-facing side of the electrode and/or incorporate materials that cause electrochemical reactions to occur within the electrode rather than on or near the user's skin. When current across the face of a dermal electrode is not uniform, current and voltage gradients are created on a user's skin and underlying tissue, causing irritation and/or discomfort. Moreover, charge imbalanced electrical stimulation waveforms generally lead to a charge-transfer regime wherein reduction-oxidation reactions occur; electrodes designed with materials (e.g., Ag—AgCl and hydrogel) so that these reactions occur in electrode layers rather than on or near the user's skin can mitigate irritation and pain, at least in part due to reducing or eliminating pH changes occurring on a user's skin.
Multi-layer electrodes may also improve the comfort of electrical simulation by increasing the uniformity of current distribution and buffering pH changes at or near the skin through redox electrochemistry in the electrodes. Multi-layer electrodes deposited onto a flexible substrate are described in U.S. Pat. No. 9,393,401, U.S. Pat. No. 9,474,891, U.S. Pat. No. 9,333,334, and PCT Patent Application No. PCT/US2015/031966, filed May 21, 2015, titled “CANTILEVER ELECTRODES FOR TRANSDERMAL AND TRANSCRANIAL STIMULATION”, Publication No. WO 2015/183690. These multi-layer electrodes significantly improve comfort of transdermal stimulation and may thus improve the efficacy and/or enjoyment of transdermal electrical neuromodulation and other forms of therapeutic or non-therapeutic transdermal electrical stimulation.
It has also been suggested that electrodes having an increased number of edges may provide an improvement in implantable electrodes. See, e.g., Golestanirad et al., (“Analysis of fractal electrodes for efficient neural stimulation”, Frontiers in Neuroengineering, Jul. 12, 2013). These electrodes are configured to provide an irregular current density profile on their surface.
When the distribution of current in Ag/AgCl electrodes such as those described above is uneven, e.g., concentrated at the edges or boundaries of the electrode, the uneven distribution causes AgCl to oxidize into Ag at the edges of the electrodes, resulting in a halo of discoloration after usage (charge transfer) and potential reduction in both uniformity of charge distribution across the electrode face and pH regulating consumptive layer function, which may lead to reduced comfort or efficacy of transdermal electrical stimulation. There is a need for electrodes that more evenly distribute current across the face of a dermal electrode to improve the comfort and safety of electrical stimulation, particularly with higher current-density electrodes, including those described by Golestanirad.
Described herein are apparatuses (e.g., devices and systems), and methods that may address at least the needs identified above.